1. GLOBAL SULFUR BUDGET [Chin et al., 1996] (flux terms in Tg S yr -1 ) Phytoplankton (CH 3 ) 2 S SO 2  1.3d DMS  1.0d OHNO 3 Volcanoes Combustion Smelters SO 4 2-  3.9d 22 10 64 OH cloud 42 818 4 dep 27 dry 20 wet dep 6 dry 44 wet H 2 SO 4 (g)

2. GLOBAL SULFUR EMISSION TO THE ATMOSPHERE [Chin et al. 2000] 2001 estimates (Tg S yr -1 ): Industrial 57 Volcanoes 5 Ocean 15 Biomass burning 1

3. FORMATION OF SULFATE-NITRATE-AMMONIUM AEROSOLS Sulfate always forms an aqueous aerosol Ammonia dissolves in the sulfate aerosol totally or until titration of acidity, whichever happens first Nitrate is taken up by aerosol if (and only if) excess NH 3 is available after sulfate titration HNO 3 and excess NH 3 can also form a solid aerosol if RH is low Thermodynamic rules: Highest concentrations in industrial Midwest (coal-fired power plants) Observed aerosol acidity in US

4. GLOBAL EMISSIONS OF AMMONIA GLOBAL UNITED STATES Ammonia, Tg N yr -1 55 2.8 [Bouwman et al., 1997]

5. SULFATE-NITRATE-AMMONIUM AEROSOLS IN U.S. (2001) Highest concentrations in industrial Midwest (coal-fired power plants) SulfateNitrate Ammonium

6. STRATOSPHERIC AEROSOL TROPOPAUSE Transport of long-lived S gases (eg. COS) Injection of volcanic ash (SiO 2, Al 2 O 3, Fe 2 O 3 ) as well as gases (H 2 S, SO 2, HCl) Aerosols in the stratosphere are long-lived due to absence of precipitation and “layered” transport (due to stability) PSCs (nitric acid / water vapor)

7. HOW COMPOSITION AND SIZE FIT TOGETHER… Image from: C. Leck

8. SURFACE AEROSOL NUMBER CONCENTRATION DecJuly Continental: > 250 cm -3 Urban/polluted: > 2000 cm -3 Marine BL: ~ 200 cm -3 [Spracklen et al., 2006] GLOMAP: 2 moment sectional model simulating sulfuric acid / sea salt

9. RAOULT’S LAW water saturation vapor pressure over pure liquid water surface water saturation vapor pressure over aqueous solution of water mixing ratio x H2O An atmosphere of relative humidity RH can contain at equilibrium aqueous solution particles of water mixing ratio

10. HOWEVER, AEROSOL PARTICLES MUST ALSO SATISFY SOLUBILITY EQUILIBRIA Consider an aqueous sea salt (NaCl) particle: it must satisfy This requires: At lower RH, the particle is solid at equilibrium, though it can also remain in metastable aqueous state

11. UPTAKE OF WATER BY AEROSOLS

12. RELATIVE HUMIDITIES FOR DELIQUESCENCE/CRYSTALLIZATION OF AEROSOLS

13. IN CONTRAST TO OZONE, HEMISPHERIC AEROSOL BACKGROUND IS NOT AN AIR QUALITY ISSUE (wrt NAAQS) TRACE-P aircraft observations over NW Pacific (Mar-Apr 2001) and GEOS-Chem model simulations …because of efficient precipitation scavenging in continental outflow P3B DATA over NW Pacific (30 – 45 o N, 120 – 140 o E) [Park et al. 2005]

14. HOWEVER, DESERT DUST CAN BE TRANSPORTED ON INTERCONTINENTAL SCALES Glen Canyon, Arizona clear day April 16, 2001: Asian dust! Annual mean PM 2.5 dust (  g m -3 ), 2001 Asia Sahara Most fine dust in the U.S. (except in southwest) is of intercontinental origin

15. LONG RANGE TRANSPORT OF DUST FROM AFRICA TO THE AMAZON (2008) [Prenni et al., 2009] Timeseries of dust @ field site N of Manaus Model simulation of the African dust plume

16. [IPCC 2007] AEROSOL CLIMATE FORCING

17. SCATTERING OF RADIATION BY AEROSOLS: “DIRECT EFFECT” By scattering solar radiation, aerosols increase the Earth’s albedo Scattering efficiency is maximum when particle diameter =  particles in 0.1-1  m size range are efficient scatterers of solar radiation

18. Mt. Pinatubo eruption 1991 1992 1993 1994 -0.6 -0.4 -0.2 0 +0.2 Temperature Change ( o C) Observations NASA/GISS general circulation model Temperature decrease following large volcanic eruptions EVIDENCE OF AEROSOL EFFECTS ON CLIMATE:

19. SCATTERING vs. ABSORBING AEROSOLS Scattering sulfate and organic aerosol over Massachusetts Partly absorbing dust aerosol downwind of Sahara Absorbing aerosols (black carbon, dust) warm the climate by absorbing solar radiation

20. AEROSOL “INDIRECT EFFECT” FROM CLOUD CHANGES Clouds form by condensation on pre-existing aerosol particles (“cloud condensation nuclei”) when RH>100% clean cloud (few particles): large cloud droplets low albedo efficient precipitation polluted cloud (many particles): small cloud droplets high albedo (1 st indirect) suppressed precipitation (2 nd indirect)

21.  Particles emitted by ships increase concentration of cloud condensation nuclei (CCN)  Increased CCN increase concentration of cloud droplets and reduce their avg. size  Increased concentration and smaller particles reduce production of drizzle  Liquid water content increases because loss of drizzle particles is suppressed  Clouds are optically thicker and brighter along ship track N~ 100 cm -3 W~ 0.75 g m -3 r e ~ 10.5 µm N~ 40 cm -3 W~ 0.30 g m -3 r e ~ 11.2 µm from D. Rosenfeld EVIDENCE OF INDIRECT EFFECT: SHIP TRACKS

22. AVHRR, 27. Sept. 1987, 22:45 GMT US-west coast NASA, 2003 Atlantic, France, Spain SATELLITE IMAGES OF SHIP TRACKS

23. Aircraft condensation trails (contrails) over France, photographed from the Space Shuttle (©NASA). OTHER EVIDENCE OF CLOUD FORCING: CONTRAILS AND “AIRCRAFT CIRRUS”